Snapshots are triggered through events so there is no special API necessary for them. To get a snapshot to fire in Studio, you can drag it from the browser in the Mixer window to the Master track of any event (see the image below). You should then see a trigger region for the snapshot which you can select to see dials for its parameters in the effects deck.

[attachment=0:25wjwc3s]snapshotcreation.png[/attachment:25wjwc3s]
You can modify a snapshot’s parameters per event, as you would with any other property (i.e. you could automate a snapshot’s parameter across an event’s parameter). The same can be done with event references by dragging an event from the Event Browser window, onto another event’s track.

Although an old question here is a further answer that I’m not sure is obvious. Looking at the UE4 FMODTV videos on using the tunnel reverb it seemed it must be possible to access snapshots in code (rather than these always being triggered by snapshot modules within events).

I don’t think it’s documented (?) but you can treat a snapshot as if it is an event in code. Suppose you have a snapshot in FMOD Studio named “ReverbSnap” you can something like this: